The present invention relates to pressure vessels for fluid storage applications. More particularly, the present invention relates to a lightweight, insulated pressure vessel for the cryogenic-compatible flexible storage of alternative fuels, such as cryogenic liquid hydrogen or compressed hydrogen gas at ambient or cryogenic temperatures, in high-efficiency alternative fuel vehicles.
Efficient fuel storage and the related matters of storage tank weight and bulk are perhaps the most significant problems associated with light-duty alternative fuel vehicles, such as hydrogen or natural gas-fueled cars.
One method of reducing the weight of a pressure vessel for lightweight vehicle application is shown in U.S. Pat. No. 5,798,156 utilizing a lightweight polymer to line a compressed gas storage vessel constructed from, for example, a graphite epoxy composite. The liner includes a thin layer of low permeability metal deposited onto the polymeric layer to reduce the permeation rate to acceptable low values. The ""156 patent, however, is limited to gas pressure vessels and does not consider, describe, or suggest cooling temperatures below that required for liquefaction of such fuels.
Additionally, low-pressure cryogenic storage tanks have also been utilized for their compactness and low weight. Conventional low-pressure cryogenic tanks typically consist of a vessel for containing a cryogenic liquid, (such as liquid hydrogen, LH2 or liquid natural gas LNG) and a jacket spaced from and surrounding the vessel. The space between the vessel and the jacket is evacuated, and a thermal insulating media placed therein such that the thermal insulating media inhibits heat transfer to the cryogenic liquid which can cause vaporization and expansion. Unfortunately, evaporative losses occur during fueling of low-pressure LH2 tanks, and during periods of inactivity due to heat transfer from the environment. And furthermore, for low-pressure LH2 storage in particular, substantial amounts of electricity are required to liquefy the hydrogen (about 40% of the lower heating value of the hydrogen). Differences between these conventional low-pressure cryogenic storage tanks and high-pressure cryogenically-insulated pressure vessels of the present invention, are discussed in the publications by Applicant entitled, xe2x80x9cThermodynamics of Insulated Pressure Vessels for Vehicular Hydrogen Storage,xe2x80x9d UCRL-JC-128388, June 1997, and xe2x80x9cAnalytical and Experimental Evaluation of Insulated Pressure Vessels for Cryogenic Hydrogen Storage, xe2x80x9d International Journal of Hydrogen Energy 25 (2000), both of which are incorporated by reference herein.
One aspect of the present invention includes a lightweight, cryogenic-compatible pressure vessel for flexibly storing fluids, such as cryogenic liquids or compressed gases at cryogenic or ambient temperatures, the pressure vessel comprising: an inner pressure container enclosing a storage volume; an outer container surrounding the inner pressure container and forming an evacuated space therebetween; a thermal insulator surrounding the inner pressure container in the evacuated space to inhibit heat transfer to the storage volume; and means for substantially inhibiting vacuum loss in the evacuated space due to fluid permeation through the inner pressure container, whereby cryogenic insulation may be maintained when storing cryogenic liquids or compressed gases at cryogenic temperatures.
And another aspect of the present invention includes a lightweight, cryogenic-compatible pressure vessel for flexibly storing cryogenic liquid fuels or compressed gas fuels at cryogenic or ambient temperatures in vehicles, the pressure vessel comprising: an inner pressure container enclosing a fuel storage volume; an outer container surrounding the inner pressure container and forming an evacuated space therebetween; a thermal insulator surrounding the inner pressure container in the evacuated space to inhibit heat transfer to the fuel storage volume; and means for substantially inhibiting vacuum loss in the evacuated space due to fuel permeation through the inner pressure container, whereby cryogenic insulation may be maintained when storing cryogenic liquid fuels or compressed gas fuels at cryogenic temperatures.